Anatomy of the Cone and Fertile Stem of Equisetum. 689 
also become torn as the stem increases in width, though not infrequently the 
torn remains of such thin-walled cells may be seen adhering to the inner 
side of the thickened ring. As the latter narrows, passing down the inter- 
node the cavity which it encloses becomes smaller, until we get a solid core 
of thickened cells lying free in the central cavity (Text-fig. 9). These 
phenomena were observed in Cones A and C, in which they were closely 
similar ; the series of sections below Cone B was not sufficiently extensive 
to show the form of the mass of dark brown cells, but the presence of such 
cells was ascertained. 
Pfitzer has described dark brown cells in the interior of the branch at 
its insertion on the stem, but he does not seem to have noticed similar 
phenomena in the main shoots. His description, which, mutatis mutandis , 
agrees with the description given above, runs thus : i In a radial longitudinal 
section through the origin of the branch the brown internal mass of the 
cylinder is seen to widen out laterally ... in such a way that it comes into 
connexion with the outer endodermis of the cylinder. 5 The cylinder 
(‘ Rohre ’) mentioned here is, of course, the ring of xyletn found in the lower 
part of the branch ; upwards this cylinder of xylem only breaks up into 
separate strands above the insertion of the first leaf-sheath of the branch, 
while below it is attached to two of the cauline bundles ; its insertion here 
is also oblique with regard to the main axis. 
E. palustre has in the internode only an external endodermis, but 
Pfitzer has shown that throughout the node there is also a common internal 
endodermis, which traced upwards and downwards passes over gradually 
into the typical pith without coming into contact with the external endo- 
dermis. He remarks that in the old stems of E. palustre all the cells 
within the inner endodermis are thickened and dark brown, and says that 
they constitute the brown diaphragm. In my young specimens the dia- 
phragm was not at all brown. Pfitzer also gives a curious description of 
the brown cells within the base of the cylinder of the branch of this species. 
The branch has an inner endodermis, the inner longitudinal walls of which 
are thick and dark brown ; the cylinder also contains thickened dark brown 
cells ; these appear first in the middle of the cylinder, and their development 
is continued upwards and downwards ; when it reaches its highest grade 
‘ the whole interior of the cylinder is filled with a dark brown mass of cells 
which either shows a dilation (“ Anschwellung ”) above or below or below 
only, and is surrounded by the unthickened external longitudinal walls 
of the (inner) endodermis’. If this description is accurate the form of the 
brown mass of cells would be that of a solid dumb-bell or of a solid normally 
oriented cone. Pfitzer also describes dark brown cells in the branch of 
E. littorale and in the stem of E. variegahtm. In the latter species, when 
the nodal wood breaks up above the departure of the traces, the outer and 
inner endodermes are replaced by special endodermes round the bundles, 
